Turkey's BIST 100 Slides as US‑Iran Tensions Hit Markets

On July 13 the BIST 100 index closed down 1.6% at 14,092 points, extending a week of declines linked to heightened U.S.–Iran tensions and concerns over the Hormuz Strait. The banking index fell 1.83% and the holding index 0.30%, while the construction sector was the top performer (+0.58%). The most active shares included Turkish Airlines (THYAO) with a volume of about 15.2 billion TL, and the biggest decliners were BIGTK, DSTKF and SVGYO, each dropping around 9.9%.

Following an intra‑day move of more than 2% lower, Borsa İstanbul activated the “uptick” (or “step‑up”) rule for short‑selling on the BIST 100 to curb sharp drops. The rule requires short‑sell orders to be executed at prices higher than the last trade, aiming to protect market stability during volatile periods.

U.S. markets mirrored the pressure: the Dow Jones slipped 0.26% to 52,498 points, the S&P 500 fell 0.79% to 7,515, and the Nasdaq dropped 1.55% to 25,873. President Donald Trump announced a renewed naval blockade of the Hormuz Strait, proposing a 20% freight surcharge, which pushed Brent crude up 9.1% to $83 and WTI to $77.7 per barrel. Analysts also noted upcoming U.S. inflation data and Federal Reserve commentary that could influence monetary policy.

Bank of America’s Turkish client sold roughly 1.6 billion TL of ASELSAN shares, contributing to a 4.7% decline in the stock. Other significant BofA‑driven sales included Turkish Airlines, ASTOR, and TUPRAS. Domestic macro data showed a May current‑account deficit of $1.459 billion but a surplus of $3.626 billion when energy and gold are excluded, factors that also weighed on market sentiment.